Currently, drainage is required on approximately 110 million acres of agricultural lands in the United States. Of this approximately 41 million acres are drained using subsurface drain tubes, 36 million acres using open ditches, and 33 million acres using other surface drainage methods. Agricultural drainage lowers the water table allowing crops to be grown on soils normally too wet for crop production due to excessive soil water conditions and inability to perform planting, harvesting or other field operations.
Conventional drainage, also referred to as free drainage, maximizes drainage by lowering water level at the drainage outlet to a depth greater than 3 feet from the soil surface throughout the year. A drawback to this practice is that it removes water even during drought conditions resulting in crop yield reduction or loss due to drought stress or increased irrigation demands. Also nutrients from the fields are lost with the drainage water to streams, rivers, lakes, and estuaries.
As a solution to this drawback, flash board risers are installed at the drainage outlet. This practice is known as controlled drainage or water table management. Control structures have individual boards that can be installed, giving the ability to raise or lower the water level to a desired depth below the soil surface. Typically the water level is kept higher (just below the root zone) during the growing season to supply water to the crops, lowered during planting and harvest operations, then raised close to the soil surface during the fallow period (winter) to reduce water and nutrient loss from the field when no crop is growing. The major drawbacks to this system are the time and effort it takes to remove or replace the boards, and leakage around the joints in the boards resulting in poor drainage control. The boards often swell and become stuck in the track of the control structure which results in the need to cut the boards out when it is time to lower the water table. This costs the farmer money when the boards need to be replaced to raise the water table again. Also there is a safety issue in removing the boards. Pressure of the upstream water on the boards may cause them to suddenly break as they are being cut possibly resulting in injury.
The system described herein overcomes the drawbacks of the previously used structures. The system replaces the wooden boards with an automated gate valve which greatly simplifies lowering the water level behind the structure. The proposed automation will free the farmer from the need to manage the day to day operation of the structure for both drainage and irrigation and improve farm safety.